cpuflags_amd64.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"internal/cpu"
     9  )
    10  
    11  var memmoveBits uint8
    12  
    13  const (
    14  	// avxSupported indicates that the CPU supports AVX instructions.
    15  	avxSupported = 1 << 0
    16  
    17  	// repmovsPreferred indicates that REP MOVSx instruction is more
    18  	// efficient on the CPU.
    19  	repmovsPreferred = 1 << 1
    20  )
    21  
    22  func init() {
    23  	// Here we assume that on modern CPUs with both FSRM and ERMS features,
    24  	// copying data blocks of 2KB or larger using the REP MOVSB instruction
    25  	// will be more efficient to avoid having to keep up with CPU generations.
    26  	// Therefore, we may retain a BlockList mechanism to ensure that microarchitectures
    27  	// that do not fit this case may appear in the future.
    28  	// We enable it on Intel CPUs first, and we may support more platforms
    29  	// in the future.
    30  	isERMSNiceCPU := isIntel
    31  	useREPMOV := isERMSNiceCPU && cpu.X86.HasERMS && cpu.X86.HasFSRM
    32  	if cpu.X86.HasAVX {
    33  		memmoveBits |= avxSupported
    34  	}
    35  	if useREPMOV {
    36  		memmoveBits |= repmovsPreferred
    37  	}
    38  }
    39
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